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Saturday, March 17, 2007

Defending the earth against asteroids

The Sky Is Falling. Really. -- by RUSSELL L. SCHWEICKART/NY Times

Tiburon, Calif.

AMERICANS who read the papers or watch Jay Leno have been aware for some time now that there is a slim but real possibility — about 1 in 45,000 — that an 850-foot-long asteroid called Apophis could strike Earth with catastrophic consequences on April 13, 2036. What few probably realize is that there are thousands of other space objects that could hit us in the next century that could cause severe damage, if not total destruction.

Last week two events in Washington — a conference on “planetary defense” held by the American Institute of Aeronautics and Astronautics, and the release by NASA of a report titled “Near-Earth Object Survey and Deflection Analysis of Alternatives” — gave us good news and bad on this front. On the promising side, scientists have a good grasp of the risks of a cosmic fender-bender, and have several ideas that could potentially stave off disaster. Unfortunately, the government doesn’t seem to have any clear plan to put this expertise into action.

In 1998, Congress gave NASA’s Spaceguard Survey program a mandate of “discovering, tracking, cataloging and characterizing” 90 percent of the near-Earth objects larger than one kilometer (3,200 feet) wide by 2008. An object that size could devastate a small country and would probably destroy civilization.

The consensus at the conference was that the initial survey is doing fairly well although it will probably not quite meet the 2008 goal. Realizing that there are many smaller but still terribly destructive asteroids out there, Congress has modified the Spaceguard goal to identify 90 percent of even smaller objects — 460 feet and larger — by 2020. This revised survey, giving us decades of early warning, will go a long way toward protecting life on the planet in the future.

The good news is that scientists feel we have the technology to intercept and deflect many asteroids headed toward Earth. Basically, if we have early enough warning, a robotic space mission could slightly change the orbit of a dangerous asteroid so that it would subsequently miss the planet.

Two potential deflection techniques appear to work nicely together — first we would deflect the asteroid with kinetic impact from a missile (that is, running into it); then we would use the slight pull of a “gravity tractor” — a satellite that would hover near the asteroid — to fine-tune its new trajectory to our liking. (In the case of an extremely large object, probably one in 100, the missile might have to contain a nuclear warhead.) To be effective, however, such missions would have to be launched 15 or even 30 years before a calculated impact.

The bad news? While this all looks fine on paper, scientists haven’t had a chance to try it in practice. And this is where NASA’s report was supposed to come in. Congress directed the agency in 2005 to come up with a program, a budget to support it and an array of alternatives for preventing an asteroid impact.

But instead of coming up with a plan and budget to get the job done, the report bluntly stated that “due to current budget constraints, NASA cannot initiate a new program at this time.” Representative Bart Gordon, Democrat of Tennessee, was right to say that “NASA’s recommended approach isn’t a credible plan” and that Congress expected “a more responsive approach” within the year.

Why did the space agency drop the ball? Like all government departments, it fears the dreaded “unfunded mandate”; Congress has the habit of directing agencies to do something and then declining to give them the money to do so. This is understandable. But in this case, Congress not only directed NASA to provide it with a recommended program but also asked for the estimated budget to support it. It was a left-handed way for the Congress to say to NASA that this is our priority ... like it or not. But for some reason NASA seems to have opted for a federal form of civil disobedience.

Another problem with the report was that, while it outlined other possibilities, it estimated that using a nuclear-armed missile to divert an asteroid would be “10 to 100 times more effective” than non-nuclear approaches. It is possible that in some cases — such as an asteroid greater than a third of a mile across — the nuclear option might be necessary. But for the overwhelming majority of potential deflection cases, using a nuclear warhead would be like a golfer swinging away with his driver to sink a three-foot putt; the bigger bang is not always better.

Why the concern? First, even with good intentions, launching a nuclear-armed missile would violate the international agreements by which all weaponry is banned from space. Second, the laws of probability say we would be struck by such a large asteroid only once every 200,000 years — that’s a long time to keep a standing arsenal of nuclear asteroid-blasters, and raises all sorts of possibilities of accidents or sabotage — the old “cure being worse than the disease” phenomenon.

In the end, of course, this is not just America’s problem, as an asteroid strike would be felt around the globe. The best course is international coordination on deflection technology, along with global agreements on what should be done if a collision looks likely. Along these lines, the Association of Space Explorers, a group of more than 300 people from 30 nations who have flown in space (of which I am a member), is beginning a series of meetings in cooperation with the United Nations to work out the outlines of such an agreement.

Still, as with many global issues, little will be accomplished unless the United States takes the lead. With the entire planet in the cross hairs, NASA can’t be allowed to dither. If Congress’s mandates and budget requests aren’t energizing the agency, perhaps public hearings would shame it into action.

(Russell L. Schweickart, a former Apollo astronaut, is the chairman of the B612 Foundation, which promotes efforts to alter the orbits of asteroids.)